1. Field of the Invention
This invention relates to a method for supporting integrated service over WLAN (wireless local area network), and more specifically, to a method for power-efficient transmission supporting integrated service over WLAN, which can reduce the power consumption for voice stations and enhance the throughput for data stations.
2. Discussion of Related Art
The integration of WLANs and 3G networks has recently evolved into a very hot topic. The service continuity is one of the issues needed to be resolved for the 3G/WLAN heterogeneous networks. In order to provide service continuity, it is essential for WLAN to support voice services. To support integrated voice and data services over WLAN, the WLAN has to support differentiated quality of services (QoSs) to guarantee the requirements of voice users. In addition to provide the differentiated QoS, the 3G/WLAN voice-enabled device needs to increase its stand-by time by reducing power consumption. Existing WLAN card may operate in either of two operation modes. In the active mode, all of the RF and based band chipsets are turning on and the power consumption is the highest. In the sleep mode, most of the functions are disabled and the power consumption could be minimized.
In order to support differentiated QoSs, the task group E of the IEEE 802.11 standardizes the MAC enhancements for WLANs, denoted as 802.11e. The IEEE 802.11e defines a hybrid coordination function (HCF) which supports a contention-based and a polling-based channel accesses. The enhanced DCF (EDCF) is the contention-based channel access, which allows the QoS access point (QAP) to exchange frames with QoS stations (QSTAs) based on CSMA/CA mechanism. The HCF controlled channel access adopts a polling-based mechanism, which allows the QAP to enable the contention-free frame exchange with the QSTAs during a contention period. Several papers such as “Voice and Data Transmission over an 802.11 Wireless Network”, M. A. Visser and M. E. Zarki, IEEE PIMRC, September 1995; “Investigate of IEEE 802.11 Medium Access Control (MAC) Sublayer Functions”, B. P. Crow, I. Widjaja, J. G. Kim, P. Sakai, IEEE INFOCOM 1997, vol. 1, pp. 126-133, 1997; and “Support of Voice Services in IEEE 802.11 Wireless LANs”, M. Veeraraghavan, N. Cocker, T. Moors, IEEE INFOCOM 2001, vol. pp. 488-497, 2001 have studied the performance of integrated voice and data services over WLANs. In these papers, the operations of WLANs are limited to a point coordinator function (PCF) and a distributed coordinator function (DCF), instead of the HCF. Moreover, a round-robin (RR) polling scheme was adopted to schedule the voice sources. It may cause power waste due to the excess polling of silent stations (STAs).
Further, U.S. Pat. No. 6,747,968, “Methods and Systems for Weighted PCF Polling Lists for WLAN QoS Support” has disclosed a weighted polling scheme considering the billing information, transmission duration and user profiles as a weighting function. However, the scheme is proposed for PCF mechanism only. U.S. Pat. No. 6,640,268 “Dynamic Polling Mechanism for Wireless Devices” has disclosed a dynamic polling scheme which adjusts the polling intervals according to the activity level of each polled device. However, the devices returning from the idle mode need to contend in the DCF mechanism to join the polling list, and whereby the polling waste occurs. U.S. Pat. No. 6,275,500, “Method and Apparatus for Dynamic Control of Talk Groups in a Wireless Network” has disclosed a method for dynamic control of talk groups. However, it only handles the communication between the talk groups and does not involve with the organization of the polling list. And U.S. Pat. No. 5,297,144, “Reservation-Based Polling Protocol for a Wireless Data Communications Network”, has disclosed a polling method for non-contention-based wireless network. However, this method cannot be used in the contention-based transmission mode.
Therefore, it is necessary to develop a method capable of application of both the PCF and DCF mechanism for integrated voice and data services over WLAN to reduce the power consumption.